Casing centralizer



, UNITED STATES PATENT OFFICE CASING CENTRALIZER Application September 22, 1939, Serial No. 296,099

8 Claims.

This invention relates to casing centralizers, being particularly concerned with centralizers of the spring type, which tend to maintain the-casing centered in the bore hole. Such centering is desirable and important to ensure that a uniform thickness of cement will be deposited around the casing for the purpose of providing an effective cementitious seal against the passage of encroaching waters or other fluids into the well or casing.

In the form of casing centralizers which embody outwardly bowed leaf springs yieldably engageable with the sides of the casing or hole, it is preferred that these springs be pulled and not pushed through any restrictions or obstructions as the casing is being raised or lowered in the hole. The pulling action assists in moving the outwardly bowed springs to an inward position permitting them to pass the restriction or obstruction with greater facility. If;='the centralizer and its outwardly bowed springs were placed under compression, or pushed, as the casing was moved through the hole, the springs would tend to buckle or collapse upon engaging an obstruction or restriction, effecting an increase in their diameter and in many cases preventing the passage of the centralizer. Attempts to move beyond the obstruction with this last-mentioned arrangement oftentimes cause failure of the springs and their consequent unavailability for further use as a centering device for the casing.

Accordingly, it is an object of this invention tc provide an improved casing centralizer which is always being pulled through the casing or hole regardless of the direction in which the casing is being moved.

It is a further object of the invention to increase the bearing area of the spring arms against the sides of the hole to minimize their tendency to dig into the formation.

Still a further object of the invention is to so shape the bowed springs of a casing centralizer as to obtain, an increased contacting surface with the formation, as well as a more uniform distribution of the load over a greater or longer portion of the spring.

The invention has other objects that will become apparent from a consideration of the embodiments shown in the drawing accompanying sndforming part of the present specification. These forms will now be described in detail, but it is to be understood that such detailed description isnot to be taken in a limited sense, since the scope of the invention is best defined by the appended claims.

Referring -to the drawing:

Figure '1 is a side elevational view of a centralizer prior to its assembly on a casing;

Figure 2 is a view similar to Figure 1, showing the centralizer assembled on a casing within a bore;

Figure 3 is a section taken along the line 33 of Figure 1;

Figure 4 is a fragmentary, partially sectional view of a modified form of centralizer; and

Figure 5 is a front elevation of a leaf spring forming part of the centralizer disclosed in Figure 4.

In its general aspects, the invention contemplates the provision of a casing centralizer embodying outwardly bowed leaf springs secured to spaced collars. Stop rings are secured to the well casing for abutting engagement with companion stops formed on the leaf springs, so that regardless of whether the casing is being lowered or raised in the hole, one of the stops will engage the springs to pull them and their associated collars through the hole, and not push them through the hole.

More specifically, the casing centralizer A consistsof spaced upper and lower collars l0, II to which a plurality of circularly spaced and outwardly bowed leaf springs 12 are secured by welding material I3 or other suitable means. The ends M of each spring extend beyond the collars and are inwardly bent to provide stops I 5 adapted to contact stop rings I611, liib, each of which is placed between the outer end of an associated collar IE or II and the bent leaf portions I 5. Each ring Isa or liib has substantially the same internal diameter as the collars, but is initially provided with a split H to permit its insertion between the bent portions l5jand a collar after the leaves have been securely welded in assembled position. Subsequent to the provision of. the stop rings Ilia, 16b between the bent springportions I5 and the collars l0, II, the entire assembly is slid or placed over a casing B and the stop rings moved to positions abutting the bent spring portions. Thereafter, the stop rings are securely attached to the casing by depositing welding material 18 around holes I9 provided in the rings and also by welding the adjacent ring ends which define the split i1 together.

It'will be noted that when a stop ring lfia or Ifib engages its cooperative bent spring stops IS a clearance space 20 remains between it and the neighboring collar. This space is allowed to permit the bowed central parts of the springs 12 to move inwardly upon their encountering of obstructions or restrictions in the casing or hole I through which they are passing, which movement produceslongitudinal motion of a collar towards its stop ring. The various parts are arranged and the clearance space predetermined to pe. rit complete inward movement of the bowed portions of the spring into engagement with the casing without any restraints being imposed by the abutting of a slidable collar III or II with a stop ring Ilia or llib.

The manner in which the centralizer A functions in the hole will now become apparent. Since the stop rings lia, llib are welded to the casing B, downward movement of this casing and centralizer will cause the lower stop ring lBb to engage the lower bent portions l5 of the springs, and thus produce a pulling force upon the bowed springs should they encounter obst'ructions or restrictions in the'hole, thereby assisting and allowing them to move inwardly toward the casing B. During this downward movement, the upper stop ring lia is ineffective, but because of the clearance space 20 between it and its adjoining collar ID the latter can move longitudinally upwards without restraint upon inward movement of the springs. Were the movement of the casing B reversed, the upper stop "in would be effective against the upper bent portions l5 of the springs to pull the centralizer through the hole and past any obstructions by assistingand permitting the bowed spring portions I2 to move inwardly toward the casing B on which the centralizer A is mounted. Accordingly, regardless of the direction in which the casing and centralizer are being moved through the hole, the.

centralizer springs will always be pulled and not pushed past obstructions or restrictions, avoiding the detrimental effects'caused by the application of compressive forces or a pushing action against the centralizer, which will cause the springs to buckle and collapse outwardly.

Due to the yieldability of the springs 12, the

casing B will be maintained centeredin the hole,

not onlywhile being moved to its intended position but also during a cementing operation, al-

- lowing a uniform thickness-of cement to be formed around the casing. I

For the purpose of minimizing or preventing the outwardly bowed portions of the leaf springs I! from digging into the sides of the hole, bearing leaves 2| can be secured, as by welding, to the median spring portions and arranged to conform generally to the curvature of the hole. This increased bearing area not only offers resistance to the tendency, of the leaves to dig into the formation, but it also increases the bending moment of the springs and causes the leaves to flatten out against the walls of the hole upon forcing of the leaves inwardly towards the casing B on which the centralizer A is mounted.

This last named function is also obtainable by forming each leaf spring as disclosed in Figure 5. The leaf I2a gradually increases in width from the collars III, II towards its center or mid-point 22. This arrangement 'not only provides a larger bearing area in the center region 22, but also causes the spring l2a to be flattened over a greater portion of its length upon' being subjected to inward thrust ,due to a decrease in hole diameter or restrictions. The accompanying increased bearing area' maintains the unit bearing pressure upon the formation at a low value despite the increased total load, which oflsets any tendency towards digging into the formation, which might'occur were the springs to maintain a bowed configuration and flatten only slightly of the centralizer springs l2 and collars III, ll.

This eflect is permitted since the stop rings I611, "5b are free to rotate with the casing 13 within the centralizer springs. As a result, when rotation of the casing becomes desirable or essential, no fear need be had that the leaves will prevent such movement by the digging of the springs into the formation.

I claim:

1. A centering device, including a pair of spaced members, outwardly bowed springs fastened to said members, and a pair of stops movable with respect to said springs, one or the other of said stops being engageable with said springs to exert pulling effort thereon regardless of the direction of longitudinal movement of said stops.

2. A centering device, including a pair of spaced, generally cylindrical members, outwardly bowed springs fastened at intervals circumferentially around said members and extending therebeyond, and a stop between each cylindrical member and the adjoining ends of said springs, the leading stop being engageable with said springs to exert a pulling action thereon regardless of the direction of longitudinal movement of said s ops.

3. A centering device, including a pair of spaced, generally cylindrical members, outwardly bowed springs circumferentially arranged around said members and secured thereto, said springs extending beyond said members with their terminal portions bent to form abutments spaced longitudinally from said cylindrical members, and stop means between each member and its associated spaced abutments, said stop means being of lesslength than the distance between said member and abutments.

4. A centering device, including a pair of spaced, generally cylindrical members, outwardly bowed springs circumferentially arranged around said members and secured thereto, said springs extending beyond said members with their terminal portions disposed inwardly to form abutments spaced longitudinally from said cylindrical members, and an annular stop between each member and its associated spaced abutments, said stop beingof less length than the distance between said member and abutments.

5. In combination with a casing, a centering device including a pair of spaced, generally cylindrical members slidable on said casing, outwardly bowed springs circumferentially arranged around said members and secured thereto, said springs extending beyond said members with their terminal portions disposed inwardly to form abutments spaced longitudinally from said cylindrical members, and an annular stop secured to said casing between each member and its associated spaced abutments, each of said stops being contiguous its abutments when said springs are in their outermost'position and-spaced from its cylindrical member by a distance sufli-. cient to permit maximum inward-movement of said springs toward said casing and unrestrained sliding of said member toward said stop.

6. A centering device, including a pair of spaced, generally cylindrical members, bowed springs fastened at intervals circumferentially around said members and extending therebeyond, and a stop between each cylindrical member and the adjoining ends or said springs, one or the other of said stops being engageable with said springs to exert a pulling action thereon regardless of the direction of longitudinal movement of said stops.

7. A centering device, including a pair of spaced members, bowed springs fastened at intervals to said members and extending therebeyond, and a stop between each member and the adjoining ends of said springs, one or the other or said stops being engageable with said springs to exert a pulling action thereon regardless of the direction of longitudinal movement of-said stops.

8. A centering device, including a pair of spaced members, bowed springs fastened to said members, and a pair of stops movable longitudinally of said springs, the leading stop being engageable with said springs to exert pulling effort thereon regardless of the direction of longitudinal-movement of said stops.

JULIEN A. WELLES. 

